1. Field of the Invention
Embodiments of the present invention generally relate to compression of quantization matrices in video coding.
2. Description of the Related Art
Video compression, i.e., video coding, is an essential enabler for digital video products as it enables the storage and transmission of digital video. In general, video compression techniques apply prediction, transformation, quantization, and entropy coding to sequential blocks of pixels in a video sequence to compress, i.e., encode, the video sequence. Video decompression techniques generally perform the inverse of these operations in reverse order to decompress, i.e., decode, a compressed video sequence.
In general, current video encoders break a picture into discrete blocks (e.g., 4×4 or 8×8) that are transformed into blocks of coefficients. Each block is then quantized by multiplying by a quantization scale and dividing element-wise by a quantization matrix. The video coding standard supported by a video encoder defines default quantization matrices for the supported transform block sizes and may also allow custom matrices to be used. If custom matrices are used, the matrices are compressed and transmitted in the coded bit stream for use in decoding.
Future video encoding standards such as the High Efficiency Video Coding (HEVC) standard currently under development by a Joint Collaborative Team on Video Coding (JCT-VC) established by the ISO/IEC Moving Picture Experts Group (MPEG) and ITU-T Video Coding Experts Group (VCEG) may support larger transform sizes (e.g., 16×16 and 32×32) in addition to the smaller transform sizes of the current standards in order to improve coding efficiency. Thus, quantization matrices of the same sizes will also be needed. If quantization matrices vary from picture to picture, significant overhead to transmit the quantization matrices will be incurred if current compression techniques are used.